Microelectronic imagers are used in digital cameras, wireless devices with picture capabilities, and many other applications. Cell phones and Personal Digital Assistants (PDAs), for example, are incorporating microelectronic imagers for capturing and sending pictures. The growth rate of microelectronic imagers has been steadily increasing as they become smaller and produce better images with higher pixel counts.
Microelectronic imagers include image sensors that use Charged Coupled Device (CCD) systems, Complementary Metal-Oxide Semiconductor (CMOS) systems, or other solid-state systems. CCD image sensors have been widely used in digital cameras and other applications. CMOS image sensors are also quickly becoming -very popular because they are expected to have low production costs, high yields, and small sizes. CMOS image sensors can provide these advantages because they are manufactured using technology and equipment developed for fabricating semiconductor devices. CMOS image sensors, as well as CCD image sensors, are accordingly “packaged” to protect their delicate components and to provide external electrical contacts.
FIG. 1 is a schematic side cross-sectional view of a conventional microelectronic imaging assembly 1 including an imaging unit 5 and a plurality of actuators 40 (shown schematically) coupled to the imaging unit 5. The imaging unit 5 includes an imaging die 10, a chip carrier 30 carrying the die 10, and a cover 50 attached to the carrier 30 and positioned over the die 10. The imaging die 10 includes an image sensor 12 and a plurality of bond-pads 16 operably coupled to the image sensor 12. The chip carrier 30 has a base 32, sidewalls 34 projecting from the base 32, and a recess 36 defined by the base 32 and sidewalls 34. The die 10 is accordingly sized to be received within the recess 36 and attached to the base 32. The chip carrier 30 further includes an array of terminals 18 on an interior surface of the base 32, an array of contacts 24 on an external surface of the base 32, and a plurality of traces 22 electrically connecting the terminals 18 to corresponding external contacts 24. The terminals 18 are positioned between the die 10 and the sidewalls 34 so that wire-bonds 20 can electrically couple the terminals 18 to corresponding bond-pads 16 on the die 10.
The image sensor 12 includes a plurality of pixels that each measure the intensity of either red, green, or blue light. Because each pixel senses only a single color, the other two colors at each pixel are interpolated from the measurements of adjacent pixels. This may produce inaccuracies in the color of the captured image. The inaccuracies are especially problematic near sharp transitions in the image and when a single color from the imaged object projects onto multiple pixels. To reduce interpolation, some electronic devices include motors or other actuators 40 for moving the imaging unit 5 to increase the resolution of the captured images. The actuators 40 shift the imaging unit 5 so that each pixel is exposed to light at several locations. For example, the actuators 40 may shift the entire imaging unit 5 such that a measurement from each of a red, green, and blue pixel is obtained for each pixel location of the image sensor 12. The measurements of the different pixels at a single pixel location are input into an algorithm to calculate the color at the location.
One problem with conventional imaging assemblies is that the combination of the imaging unit and actuators has a relatively large footprint and occupies a significant amount of vertical space (i.e., high profile). For example, the footprint of the imaging assembly 1 in FIG. 1 is the surface area of the actuators 40 and the base 32 of the chip carrier 30, which is significantly larger than the surface area of the imaging unit 5. Accordingly, the footprint and vertical profile of conventional imaging assemblies can be limiting factors in the design and marketability of digital cameras, picture cell phones, or PDAs because these devices are continually being made smaller in order to be more portable. Therefore, there is a need to provide imaging assemblies with smaller footprints and lower vertical profiles.